A manufacturing method for a semiconductor light switch having a semiconductor light amplifier section and a semiconductor waveguide integrated on the same substrate has been disclosed in IEEE Photonics Technology Letters, vol. 2, pp. 214-215, March 1990.
With this method, thin layers of a predetermined semiconductor are successively laminated on the entire surface of a semiconductor substrate so as to correspond to the layer structure of a light amplifier section to be formed in order to form a lower cladding layer, a core layer, and an upper cladding layer. Then, the laminated body of the semiconductor thin layers in the area other than the area in which a light amplifier section is to be formed is etched and removed to expose the surface of the substrate, and thereafter thin layers of a predetermined semiconductor are successively laminated on the exposed surface of the substrate so as to correspond to the layer structure of a waveguide to be formed in order to form a lower cladding layer, a core layer, and an upper layer.
Subsequently, a switching section is formed by diffusing, for example, Zn in a predetermined area of the waveguide, the entire construction is etched to form a ridge-shaped waveguide having the same width, a desired pattern, and a desired height in the upper cladding layers of the laminated bodies corresponding to the light amplifier section and the waveguide, respective electrodes are mounted on the switching section and the light amplifier section, and a common electrode is mounted on the back surface of the substrate.
In this semiconductor light switch, the waveguide and the light amplifier section formed in a ridge shape have an equal path width. Switching operation is performed by injecting electric current to the switching section of the waveguide, whereas light amplification is performed by injecting electric current to the light amplifier section.
Japanese Patent Laid-Open No. 2-199430 discloses a semiconductor light switch which has waveguides of an equal width crossing in an X form, a bypass waveguide formed between the input port and the output port of respective waveguides and having a width equal to that of the aforesaid waveguide, and a light amplifier section formed on the bypass waveguide. The sectional construction of the waveguide, light amplifier section, and switching section of this semiconductor light switch is similar to that disclosed in IEEE Photonics Technology Letters.
In any of the light switches of two kinds described above, the confinement of light transmitted to the core layer at the waveguide and light amplifier section is effected by the equal-width ridges formed in the respective upper cladding layers.
For the light switches of this construction, the path width of the core layer through which light is substantially transmitted is equal for the waveguide and the light amplifier section. For this reason, the effect of confining the injected current is small when electric current is injected to the light amplifier section; therefore, it is difficult to increase the current density of the injected current. As a result, it is difficult to achieve highly efficient light amplification.